Isomerization of n-butene



United States Patent 3,345,428 ISOMERIZATION 0F N-BUTENE Brian Patrick McGrath, Crowthorne, and Leonard Turner, Waking, England, assignors to The British Petroleum Company Limited, London, England, a corporation of England No Drawing. Filed Aug. 26, 1965, Ser. No. 482,934 Claims priority, application Great Britain, Sept. 18, 1964, 38.166/ 64 6 Claims. (Cl. 260--683.2)

ABSTRACT OF THE DISCLOSURE This invention relates to a process for the isomerization of olefinic hydrocarbons and particularly to the interconversion of lower mono-olefinic hydrocarbons such as butenes. The process of the present invention comprises contacting a butene feed at elevated temperatures with a catalyst comprising a silicofluoride treated alumina.

It is to be understood that the term interconversion includes both the conversion of n-butenes to isobutene and the conversion of isobutene to n-butenes.

Fluorinated alumina catalysts are in general known to effect various hydrocarbon conversions, and in co-pending U.S. application Ser. No. 479,000 filed August 11, 1965 it is stated that in order to obtain a high level of selectively for the interconversion of butenes, the fluorinated alumina catalysts used must satisfy certain criteria. It has been found that not all aluminas give rise to satisfactory catalysts and that only those which have a specified reversible benzene adsorption as hereinafter defined give rise to satisfactory catalysts. Further it has been found that the percentage weight of fluorine retained on the specific aluminas must be within'certain limits if satisfactory catalysts are to be obtained.

Apart from fluorinated aluminas, it is also known that aluminas treated with silicofluoride ions will in general effect various hydrocarbon conversions.

It has now been found that in order to effect the interconversion of butenes with a high level of selectively, the silicofluoride treated aluminas should satisfy certain criteria.

Accordingly the present invention constitutes a modification of the invention described in U.S. application Ser.

No. 479,000 filed August 11, 1965 and provides a process for the interconversion of butenes comprising contacting the butene feed at elevated temperature with a catalyst comprising a silicofluoride treated alumina containing 0.5 to 3.5 percent by weight of the said anion, said alumina having a reversible benzene adsorption as hereinafter defined, measured at a benzene pressure of 0.11 mm. of mercury and a temperature of 190 C., of at least 2 mols of benzene per gram of alumina. The use of reversible benzene adsorption criteria to assess the suitability of various aluminas for use in the low temperature isomerization of C and higher parafiinic hydrocarbons is described in pending UK. patent application No. 42,830/62.

It is to be understood that whenever catalysts are defined or characterized by anion content the content specified is the theoretical content calculated from the quantity of anion added to the alumina during the preparation of the catalyst.

The reversible benzene adsorption is a measure of acidity, low figures indicating a low acidity. The measurement of the benzene adsorption of an alumina involves contacting the alumina with benzene vapour at a low partial pressure and a fixed temperature and measuring the amount of vapour adsorbed and desorbed. The amount of the benzene adsorbed may vary with the test condi- 3,345,428 Patented Oct. 3, 1967 tions used, and in particular with the partial pressure of the benzene vapour and the temperature. It is thus necessary to standardise the conditions and for the purpose of the present invention the partial pressure used is 0.11 mm.

mercury and the temperature 190 C.

One description of a suitable technique for measurement of benzene adsorption and an apparatus therefor is to be found in a paper by R. C. Pitkethly and A. G. Goble entitled: The Adsorption of Benzene on Supported Platinum Catalysts and published in Actes du Deuxieme Congres Internationale de Catalyse Paris 1960, volume 2, at page 1851. Adsorption at low partial pressure is normally attributable to chemisorption with a relatively small contribution from physical adsorption and the apparatus for measuring it has three principal sections, viz:

(a) A vapour introduction device;

(b) A holder for the solid to be tested;

(c) A vapour detector.

The vapour introduction device has a source of carrier gas, for example nitrogen or hydrogen, .a container for the material to be adsorbed and a valve allowing either the gas alone or gas containing very small quantities of the material to be adsorbed to pass over the solid. The holder which contains the catalyst or catalyst support is capable of being held at a constant temperature over a wide temperature range. Gas passing over the catalyst then. goes via the sampling valve to the vapour detector which may be a hydrogen flame-ionization detector. The detector system may have gas chromatographic columns if the relative rates of adsorption of different materials are to be determined or if reaction is likely under the conditions of test and the composition of the reaction product is to be determined. This is not likely to apply to the present invention.

By passing a stream of gas containing material to be adsorbed over the catalyst or catalyst baseto be tested and measuring the difference between the amount of material fed to the catalyst or catalyst base and the amount vpassing to the detector, the amount of material adsorbed can be determined, after a small correction for dead space in the system. If the flow .of material is then discontinued and gas alone is passed over the catalyst, the amount of material which can be desorbed can also be determined. The amount desorbed is known as the revers'ible adsorption; the difference between the amount adsorbed and desorbed is known as the irreversible adsorption. I

The carrier gas for the benzene vapour should be inert to alumina and is, preferably, nitrogen.

The aluminas to be tested are desirably given a standard pretreatment to bring them to a standard chemical and physical state and eliminate any effects which could be due, for example, to different water contents. Prolonged heating in an inert atmosphere is preferred, for example heating between 800 C. in dry nitrogen for from 1-75 hrs. A particularly preferred pretreatment is heating at 470 C. for 16 hrs. in dry nitrogen.

Aluminas suitable for use in the present invention have a reversible benzene adsorption of at least 2,LL'IT101S of benzene per gram of alumina under the specified conditions of measurement, preferably the reversible benzene adsorption is at least 3.5 mols per gram.

The catalysts used in the process of the present invention should have a silicofluoride content of 0.5-3.5% by wt. Catalysts containing more than 3.5% by wt. of the anion gives rise to high proportions of cracked and polymeric products to the detriment of the desired butene isomers. Preferably the proportion of the anions present in the catalysts is 1.02.5% by wt.

The catalysts used in the present process may be prepared by slurrying the selected alumina with an aqueous solution of the free fluoro-silicic acid or preferably with an aqueous solution of the corresponding ammonium salt.

The amount of acid or salt used is calculated to give the required amount of the silicofiuoride anion in the finished catalyst. The slurries are then dried, e.g., at about 110 C. and calcined,'e.g., at 450 C. in a flow of nitrogen for about 3 hours.

The process of the invention, as mentioned above, is applicable both to the conversion of n-butenes to isobutene and to the conversion of isobutene to n-butenes. There fore, the feed to'the process may comprise any butene isomer or mixture of isomers, providing that the mixture is not the equilibrium mixture corresponding to the reaction conditions employed. Preferably the feed will have a low diene content.

The process is effected at elevated temperature and generally temperatures in the range 250550 C. will be used. Pressures may be sub-atmospheric, atmospheric or super-atmospheric, and the g.h.s.v. of the feed may be in the range 100 to 10,000 v./v. Preferably the feed olefin is admitted to the reactor in admixture with a diluent gas for example an inert gas such as nitrogen.

The invention is illustrated by the following examples.

Examples 1 to 5 An alumina having a reversible benzene adsorption of 176 mols benzene per gram alumina, measured at a partial pressure of benzene of 0.11 mm. mercury at 190 C. after a pretreatment consisting of heating at 470 C. for 16 hours in dry nitrogen, was treated with ammonium silicofiuoride to give catalyst containing from 0.5 to by weight of the silicofluoride ion SiF In all the examples, the feed, a mixture containing 99.0% by wt. n-butenes, 0.8% by wt. n-butene and 0.2% by wt. C was passed with nitrogen in the mol ratio of 2:1 over the catalyst at a total g.h.s.v. of 1500 v./v. at 450 C. and the aqueous products analysed after 1 hour. The results are set out in Table 1 below.

Examples 6 and 7 are comparative only. In the former the catalyst had a silicofluoride ion content of 10% by wt. which is outside the scope of the present invention. In the latter the alumina had a reversible benzene adsorp tion under the previously specified conditions of 1.65 mol/g, which is also outside the scope of the present invention.

It will thus be seen that catalysts containing less than 1.0% by wt. SiF are relatively inactive for butene conversion whilst with those containing more than 3.5% by wt. SiF selectivity to butene interconversion is relatively low due to excessive side reaction. In the range 1.03.5% by wt. SiF high isomerization activity is coupled with relatively little side reaction.

It will also be noted that the alumina with a benzene adsorption of 1.65; mol/ g. gave an inactive catalyst.

We claim:

1. A process for the isomerization of n-butenes to recover isobutene which comprises contacting the n-butene feed at elevated temperature with a catalyst, consisting essentially of a silicofluoride treated alumina containing 0.5-3.5 by wt. of the SiF anion, said alumina having a reversible benzene adsorption measured at a benzene pressure of 0.11 mm. of mercury and a temperature of 190 C. of at least 2 mols of benzene per gram of alumina.

2. A process according to claim 1 wherein the proportion of silicofiuoride present in the catalyst is 1.0-2.5% by wt.

3. A process according to claim 1 wherein the catalyst is prepared by slurrying the alumina with an aqueous solution of free fluosilicic acid or of the ammonium salt thereof.

4. A process according to claim 1 wherein the temperature is in the range 250550 C.

5. A process according to claim 1 wherein the g.h.s.v. of the feed is in the range 10,000 v./v.

6. A process according to claim 1 wherein isomerization is effected in the presence of an inert gas.

References Cited dustrial and Engineering Chemistry, vol. 39, No. 11, pages 1462-66, 1947.

DELBERT E. GANTZ, Primary Examiner.

R. H. SHUBERT, V. OKEEFE, Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,345,428 October 3, 1967 Brian Patrick McGrath et a1,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, lines 29 and 42, for "selectively" each eccurrence, read selectivity column 3, line 35, for aqueous read gaseous Signed and sealed this 14th day of January 1969.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

1. A PROCESS FOR THE ISOMERIZATION OF N-BUTENES TO RECOVER ISOBUTENE WHICH COMPRISES CONTACTING THE N-BUTENE FEED AT ELEVATED TEMPERATURE WITH A CATALYST, CONSISTING ESSENTIALLY OF A SILICOFLUORIDE TREATED ALUMINA CONTAINING 0.5-3.5% BY WT. OF THE SIF6**2- ANION, SAID ALUMINA HAVING A REVERSIBLE BENZENE ADSORPTION MEASURED AT A BENZENE PRESSURE OF 0.11 MM. OF MERCURY AND A TEMPERATURE OF 190*C. OF AT LEAST 2 MOLS OF BENZENE PER GRAM OF ALUMINA. 